How can I tell if a Caster Wheel is made of rubber or polyurethane?

I have a lot of wheels that I want to sell, but do not know if the wheels of rubber or polyurethane. Is there any evidence or touch the main visual difference / between the two materials that will help me determine what are those facts?

Rubber strain crystallizes. One of you put wheels under intense pressure, for example a press, then, if it crystallizes, which means they shatter, then you have rubber. Both materials are polymers and this is the only way I can think of giving the information I have. Hopefully, a expert will come and handle this.

36 New 2″ Caster Wheel With Swivel Base rubber wheels $44.99

12 pc 2″ Caster Wheel W/ Swivel Base rubber wheels $9.99

4 PC 3″ RUBBER CASTER WHEELS 2 FIXED AND 2 SWIVEL TSF80 $19.99

Set of 4 Swivel TPR Gray Rubber Casters 4″x1-1/4″ Wheel $19.88

12 PC 3” RUBBER CASTER WHEELS 6 FIXED AND 6 SWIVEL SET $19.99

Swivel Stem Casters for Wire Shelving System Rubber $52.99

24 pcs 2″ Caster Rubber Wheels 12 swivel 12 Stationary $37.99

36 pcs 2″ Caster Rubber Wheels 18 swivel 18 Stationary $44.99

Albion 5″ Hard Rubber Rigid Caster-Use in Garage & Shop $5.30

Albion 5″ Hard Rubber Swivel Caster with Face Brake $7.95

Albion 5″ Hard Rubber Rigid Caster-XL Top Plate! $5.72

Albion 5″ Hard Rubber Swivel Caster – XL Top Plate! $6.47

Albion 5″ Gray Rubber Swivel Caster w/Total Lock Brake! $9.48

12 RUBBER 3″ SWIVEL CASTER WHEELS BASE & WHEEL BEARINGS $19.99

12 NEW 2″ CASTER RUBBER WHEELS 6 SWIVEL 6 FIXED SET $24.99

12 NEW 2″ CASTER RUBBER WHEELS 6 SWIVEL 6 FIXED SET $24.99

12 RUBBER 3″ SWIVEL CASTER WHEELS BASE & WHEEL BEARINGS $19.99

36 New 2″ Caster Wheels With Swivel Base rubber wheels $42.99

10″ FIXED Caster with FLAT-FREE (rubber) Wheel $25.86

4 PC 3″ RUBBER CASTER WHEELS 2 FIXED AND 2 SWIVEL TSF80 $19.99

Waxman Titan 2″ Rubber Stem Caster w/Brake $5.50

Waxman Titan 2″ Rubber Stem Caster $5.50

Waxman Titan 2” Rubber Swivel Plate Caster $5.00

Lot 4 Colson 5″ Ellectrically Conductive Rubber Casters $24.99

Rubber Swivel Wheel Office Chair Caster Set of 5 – 132 $13.80

Waxman Titan 2” RUBBER PLATE CASTER $5.50

12 PC 3″ 6 Swivel and 6 Fixed Caster Rubber Wheels $19.99

12 NEW 2″ CASTER RUBBER WHEEL 6 SWIVEL 6 FIXED SET $24.99

8 PC 3″ RUBBER CASTER WHEELS 4 FIXED AND 4 SWIVEL SET $14.99

Hogdman Caster Rubber Chest Waders Size 10 Worn Once $0.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders sz12 $10.99

12 pc 2″ Caster Wheel W/ Swivel Base rubber wheels $12.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders $44.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders $44.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders $44.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders $44.99

Hodgman Caster Cleated Boot Foot Rubber Hip Waders $44.99

SOFT WHEEL RUBBER CASTERS FOR ALL HARD FLOORS GRAY 5PCS $6.50

24 NEW 2″ CASTER RUBBER WHEEL 12 SWIVEL 12 FIXED SET $37.99

24 NEW 2″ CASTER RUBBER WHEELS 12 SWIVEL 12 FIXED SET $37.99

16 PC 3″ 8 Swivel and 8 Fixed Caster Rubber Wheels TOOL $39.99

4 PC 6″ RUBBER CASTER WHEELS 2 SWIVEL AND 2 FIXED RW-06 $29.99

4 PC 6″ RUBBER CASTER WHEELS 2 SWIVEL AND 2 FIXED $29.99

36 NEW 2″ CASTER RUBBER WHEELS 18 SWIVEL 18 FIXED SET $44.99

12 RUBBER 3″ SWIVEL CASTER WHEELS BASE & WHEEL BEARINGS $19.99

12 pc 2″ Caster Wheel W/ Swivel Base rubber wheels $12.99

WISE Wesco Moldon Rubber Casters Steel Trucks 5×2 NEW $59.17

WISE Wesco Moldon Rubber Casters Steel Trucks 6×2 NEW $62.62

WISE Moldon Rubber Casters For Aluminum Trucks 6×2 NEW $220.89

WISE Moldon Rubber Casters For Aluminum Trucks 8×2 NEW $247.20

10 OFFICE CHAIR RUBBER CASTER SOFT WHEEL LAMINATE FLOOR $19.95

12 pc 2″ Caster Wheel With Swivel Base rubber wheels $22.99

50 OFFICE CHAIR RUBBER CASTER SOFT WHEEL LAMINATE FLOOR $79.95

200 OFFICE CHAIR RUBBER CASTER SOFT WHEEL WOOD FLOORS $199.95

24 NEW 2″ CASTER RUBBER WHEEL 12 SWIVEL 12 FIXED SET $37.99

Step Stool with Safety Casters, Rubber Tread, 500 lb Capacity, Silverstone CRA100101 $47.99 Easy to move, all-steel, time-tested classic. Easy to move with retractable, locking casters. No slip rubber tread on all steps. Protective bumper. 500 pounds download rating. Silverstone….

Shepherd 9610 6-Inch x 1-1/2-Inch Plastic Hub Semi-Pneumatic Rubber Diamond Tread Replacement Wheel With 1/2-Inch Bore $5.17 Shepherd Hardware 9610 Plastic Hub Semi Pneumatic Rubber TiresShepherd Hardware 9610 Plastic Hub Semi Pneumatic Rubber Tires Features:; Multi purpose replacement; A selection of the most commonly used household, industrial, lawn, garden and material handling wheels; Economical rust free plastic hubs; Pneumatic tires; Diamond tread; 1/2″ bore; Carded; 9610: 6″ x 1-1/2″; 9611: 7″ x 1-1/2″…

Steel Folding Chairs with Padded Seat – Light Beige (Set of 4) $90.65 HONFC02LBG Sturdy steel gray tube frame. Rubber caps protect flooring. 17w x 17d x 35h. Global Product Type: Chairs/Stools-Chairs without Casters; Features & Functions: N/A; Seat Type: Padded; Seat Width: N/A.PRODUCT DETAILS: -Upholstery Color: Light Beige. -Overall Width : 16 3/4 in. -Base/Frame Color/Finish: Light Beige. -Caster/Glide/Wheel Type: Rubber Caps. -Overall Height Maximum : 29 1/4 in…

Slipstick CB650 Heavy Duty Bed Risers, Chocolate $16.25 From the Manufacturer Heavy Duty 5-1/4-Inch Bed Risers holds up to 2,000 lbs with set of 4 (or 500 lbs per riser). Each riser holds caster wheels or posts up to 3-Inch, with a special non-slip rubberized bottom….

Steelex D2598 3-Inch 150-Pound Swivel Double Lock Rubber Plate Caster, Gray $6.20 Double braking system is easily engaged with a flick of the foot. Locks the movement of the wheel and the swivel. Threaded stud measures M12-1.75 x 28mm….